Fig. 4.

Nanoscale mapping of axon caliber. a Validation of axon caliber, as measured by SpeRe. Diameters of axons from the brain (n = 16) and the spinal cord (n = 8) were quantified using both SpeRe and a fluoromyelin-based method. The red dotted line indicates the unity line (R ² = 0.93). b A nanoscale volumetric view of the axon. The image stack (xyzλ) is skeletonized and rendered using the axon diameter extracted from wavenumber period $\left({\tilde{\nu }}_p\right)$ for each pixel on the skeleton. Myelin is not shown. c Probability density function of axon diameter acquired from b. The diameter is quantified for each 1.2 μm axon segment. The dotted line indicates the best fit to log-normal distribution (geometric mean = 0.52 μm, geometric standard deviation = 0.37)